1. Field of the Invention
The present invention relates to a tubular lining material for city water pipe lines, chiefly those buried in the ground. More particularly, the present invention relates to a tubular lining material utilizable for repair or reinforcement of city water pipe lines, especially those already constructed and buried in the ground, which comprises a tubular textile jacket overlaid with a coat of a selected synthetic resin which is not only satisfactory in mechanical strength but also harmless to drinking water and is applied onto the inner surface of the pipe lines according to the so-called "evagination-lining" method.
2. Description of the Prior Art
In recent years, a tubular lining material was used for the purpose of repair and reinforcement of superannuated pipe lines which had been constructed and buried in the ground. In case of underground pipe lines such as gas conduits, water pipe lines, oil pipe lines, sewage pipes made of concrete or porcelain and pipe lines enclosing power transmission wires or telecommunication cables, their superannuation or damage thereto often causes dangerous leakage of combustible fluids or electricity and unexpected rupture of water, thus resulting in serious accidents and traffic disturbance. As pipe-exchange work especially for underground pipe lines to prevent such problems involved much cost and difficulty, the use of a tubular lining material for repairing and reinforcing the pipe lines is in wide use. A method for lining pipe lines with a resin-coated tubular textile jacket as a tubular lining material has also been improved upon several times and a typical one now advantageously utilized is disclosed, for example, in U.S. Pat. Nos. 4,334,943, 4,368,091 and 4,350,548 and generally comprises the steps of applying a binder onto the inner surface of a tubular lining material having a resinous coat on the exterior surface thereof, passing the tubular lining material in flattened state through a pipe line and evaginating the tubular lining material within the pipe line under fluid pressure while allowing the lining material to advance within the pipe line and simultaneously bonding the evaginated tubular lining material onto the inner surface of the pipe line by the aid of a binder with or without the use of a leading rope-like elongated material, such as a belt, which has previously been passed through the tubular lining material beyond its full length and is drawn from the opposite end of the pipe line. The method disclosed in these patents is generally called the "evagination-lining method" and is considered to be the most desirable of the existing pipe-lining methods, particularly in that such lining material can easily be inserted into pipe lines to be treated and is applicable to pipe lines having a plurality of bends or curved portions within a short period of time irrespective of the length and diameter of the pipe lines.
A tubular lining material utilizable for such evagination-lining method should be flexible, air-impervious and satisfactory in strength in both longitudinal and lateral directions. Thus, a tubular lining material suitably used for this lining method is a tubular textile jacket made of warps and a weft woven (or knitted) in a tubular form overlaid with an air- or fluid-impervious coat of a flexible synthetic resin. On application of the lining material onto the inner surface of the pipe line according to the evagination-lining method, a binder is first applied onto the inner surface of the tubular lining material. At this stage, the lining material is provided on the exterior surface thereof with the resinous coat and on the inner surface thereof with a layer of a binder to form a three-layered structure and is kept in a flattened state so that the lining material may be smoothly inserted into the pipe line with or without the aid of a leading belt. The lining material is then allowed to advance within the pipe line while turning the lining material inside out (evagination) under fluid pressure whereby the evaginated lining material is bonded onto the inner surface of the pipe line with the binder being interposed between the pipe line and the tubular textile jacket, exposing as the innermost wall of the pipe line the resinous coat which prevents any leakage of a fluid passed through the pipe line and has a smooth surface capable of reducing friction between the pipe line and the flowing fluid to assure smooth flow of the fluid. Thus, a synthetic resin used as the resinous coat of the lining material should have flexibility and moderate stretchability and strength and is excellent in heat-resistance, abrasion-resistance and water-resistance. In case the lining material is used for city water pipe lines, however, the synthetic resin constituting the resinous coat is required to be physiologically safe under the regulations for drinking water. In Japan, synthetic resins utilizable for city water pipe lines are specified in the specifications established by the Japan Water Works Association (JWWA) organized by all the public enterprises for city water. Prior to actual use, pipes and the incidental materials used for city water should obtain a type certificate from JWWA. Thus, synthetic resins used as the resinous coat of the lining material must also satisfy the requirements defined in the specifications established by JWWA. On the other hand, drinking water supplied from such city water pipe lines has to satisfy the requirements specified in the various test items in the regulations of the Ministry of Health and Welfare relating to the standard of drinkable water under the provision of Article 4, Par. 1 of the City Water Law. Similar requirements for the quality of drinkable water are also seen in other countries. In the U.S.A., for example, the first relevant law named "the Safe Drinking Water Act" (Public Law 93-523) was enforced by the U.S. Congress in 1974 for all the federal public agencies for city water, and subsequently "the National Interim Primary Drinking Water Regulations" and "the Secondary Drinking Water Regulations" were proposed as guidelines for checking the quality of drinking water and are enforceable by the U.S. Environmental Protection Agency (USEPA). In addition, similar severe standards of drinking water were established by European countries and WHO and some regulations are put in force to protect public health. In any country, therefore, materials used for supply and storage of drinking water have to meet the severe requirements specified in the worldwide common regulations.
According to the specifications established by JWWA, lining materials for city water pipe lines are regarded equivalent to tar epxoy resin paints applicable to the inner surface of city water pipe lines. Thus, the regulations "Tar Epoxy Resin Paints for Water Works and Method of Coating" (K 115-1974) are applied to the examination of lining materials for city water pipe lines. In order that resin-coated lining materials are utilizable for repairing or reinforcing city water pipe lines under the regulations K 115-1974, the following properties are required for drinking water passed through the resin-coated lining materials:
(1) To be 0.5 or less in turbidity
(2) To be 1 or less in color scale
(3) to be 0.7 ppm or less in the amount of potassium permanganate consumed
(4) To be 0.7 ppm or less in the amount of residual chlorine reduced
(5) To have a phenol content of 0.005 ppm or less
(6) To show no detection of amines
(7) To show no detection of cyanides
(8) Not to be abnormal in odor and taste.
Polyurethane elastic resins, polyester elastomers and the like synthetic resins used as a resinous coat on the tubular lining materials for ordinary gas conduits fail to meet the above requirements as these resins can impart, for example, any residual amine to drinking water passed through the lined pipe line.
Thus, the present inventors have extensively researched various synthetic resins to check what kind of resin could satisfy the test items required for materials utilizable for city water pipe lines. As a result of the research, it was found that synthetic resins utilizable for this purpose were limited only to fluororesins and resins of the polyolefin series. Of these utilizable synthetic resins, the fluororesins are expensive and poor in extrusion characteristics and are thus inappropriate for the purpose of this invention. Consequently, synthetic resins utilizable as the resinous coat of the lining material for city water pipe line are inevitably limited only to those of the polyolefin series.
In general, the resins of polyolefin series involve, for example, high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), atactic or isotactic polypropylene (PP) and polybutene-1 (PB). Among these polyolefins, HDPE and MDPE are devoid of flexibility, while LDPE is poor in stress-crack resistance, PP is poor in flexibility irrespective of whether it is crystalline or amorphous, and the heat-resistance property of PB deteriorates and shows a "whitening" phenomenon at a turning point on evagination when used as a resinous coat on the lining material according to the evagination process. Thus, these polyolefins are advantageous in some aspects but disadvantageous in others.
In recent years, linear low density polyethylene (LLDPE) is being watched in the field of manufacturing lining materials for city water pipe lines since LLDPE possesses a combination of flexibility, as seen in LDPE, and good abrasion-resistance and stress-crack resistance as seen in HDPE. This LLDPE is a polyolefin containing predominantly polyethylene, which is obtainable by copolymerization of ethylene with a smaller proportion of an .alpha.-olefin, and belongs, as per density, to a group of low density polyethylenes (LDPE). This LLDPE has such a molecular structure that it has a very small number of long chain branches and is similar to a purely linear high density polyethylene. Consequently, LLDPE is excellent in not only tensile strength and elongation but also in stress-crack resistance and is harmless to drinking water. These useful properties make LLDPE particularly suitable as a resinous coat of the lining material for city water pipe lines.
Having discovered such excellent characteristics of LLDPE, the present inventors have already devised a tubular lining material using LLDPE as a resinous coat thereof (Japanese Utility Model Appln. No. Sho. 58-176565). Although LLDPE itself exhibited excellent mechanical strength as a resinous coat of the lining material, there were found some problems in the tubular lining material of that utility model, especially in the event the resin is used as a resinous coat on a tubular textile jacket as the substrate. As LLDPE has a Shore D hardness as high as 50, it may not be said to be a satisfactorily flexible resin. For this reason, it was somewhat difficult to evaginate the tubular lining material, onto which LLDPE had been applied as a resinous coat, under normal conditions adopted in the evagination-lining method. If the fluid pressure necessary for evagination is elevated or the drawing force acting on a leading belt for the lining material is increased in the evagination-lining method to facilitate evagination, it will apparently cause damage to the tubular textile jacket. In this lining method, the lining material evaginated and attached to the inner surface of the pipe line is heated at the final stage to cure a binder interposed between the lining material and the pipe line as a result of the evagination. This heat treatment is usually carried out by passing steam through the lined pipe line. As LLDPE is not so high in heat resistance, however, the innermost resinous coat undergoes partial fusion during this heat treatment to incur possibility the forming of pin holes in the resinous coat. Thus, the tubular lining material of this utility model still leaves a problem to be solved.
Under the above circumstances, there is still a great demand for developing a new tubular lining material for city water pipe lines, which can overcome the above mentioned drawbacks.